1. Field of the Invention
This invention relates to a high-pressure phase boron nitride for cutting tools capable of using in the cutting of high-hardness quenched steel, hard-cutting iron-based material or the like and a method of producing the same.
2. Description of the Related Art
As the high-pressure phase boron nitride, there are two types of cubic system and wurtzite, which have a hardness next to diamond and are usable as a tool material for polishing, grinding and cutting iron-based materials.
In general, cubic boron nitride (cBN) is synthesized under a statically super-high pressure using a catalyst (statically super-high pressure process), while wurtzite type boron nitride (wBN) is synthesized under an impact super-high pressure through explosion of explosive compound or the like without catalyst (impact super-high pressure process).
There are known the following sintered body containing the above high-pressure phase boron nitride and a method of producing the same.
In JP-A-57-67081 is disclosed a high hardness sintered body containing (1) 10-90 volume% of high-pressure phase boron nitride, (2) 89-9 volume% of titanium carbonitride Ti(C,N) in which an atomic weight of C is larger than that of N, and (3) not less than 1 volume% in total of aluminum and aluminum nitride. Furthermore, there is described a method of producing such a high hardness sintered body by subjecting the above mixture to a sintering treatment at a temperature of not lower than 1200.degree. C. under a pressure of not less than 4 GPa.
On the other hand, JP-A-54-66910 discloses a sintered body for a high hardness tool obtained by hot-pressing (1) wBN and (2) a carbonitride represented by M(C,N).sub.1.+-.x when a metal of Group 4a, 5a in Periodic Table is M in which an atomic volume ratio of nitrogen and carbon bonded to the metal M is N.gtoreq.C, or (1') wBN and (2') powder of a compound mainly composed of nitride represented by MN.sub.1.+-.x at a high temperature under a high pressure, wherein the sintered body comprises not less than 10 volume% in total of high-pressure phase boron nitride consisting of wBN and cBN converted from a part or whole of wBN in the sintering and the balance being mainly a compound of M and this compound is a solid solution of M--N--O or M--N--C--O in the sintered body. And also, there is disclosed a sintered body for a high hardness tool in which the above sintered body contains not less than 0.1% by weight in total of Al and/or Si in form of an intermetallic compound existing on phase diagrams of M--Al and M--Si.
In the sintered body of JP-A-57-67081, however, the preset range of each of N and C is wide, so that free carbon is created or brittle compound is formed and hence the sintered body exhibiting an excellent cutting performance is not obtained.
In the sintered body of JP-A-54-66910, N.gtoreq.C is preferable as compared with N.gtoreq.C in the carbonitride M(C,N).sub.1.+-.x because the abrasion resistance and hardness of solid solution formed in the sintered body are excellent and the roughness of cut surface after the cutting is good and the occurrence of free carbon resulting in the formation of pores is relatively small. Even in this case, the sintered body is not yet sufficient in the abrasion resistance and cutting performance, so that it is required to have a higher cutting performance.